Material for organic electroluminescent element and organic electroluminescent element using the same

ABSTRACT

Provided are a material for an organic EL device that improves the luminous efficacy of a device, sufficiently secures its driving stability, and has a simple construction, and an organic EL device using the material. The material for an organic EL device is formed of a carborane compound having a structure in which a dibenzofuranyl group is bonded to a carborane ring. In addition, the material for an organic EL device is preferably used in a light-emitting layer, an electron-transporting layer, or a hole-blocking layer of an organic electroluminescent device having the light-emitting layer between an anode and a cathode laminated on a substrate. Also disclosed is an organic electroluminescent device using the material for an organic EL device as a host material for a light-emitting layer containing a phosphorescent light-emitting dopant and the host material.

TECHNICAL FIELD

The present invention relates to an organic electroluminescent deviceusing a carborane compound as a material for an organicelectroluminescent device, and more specifically, to a thin film-typedevice that emits light by applying an electric field to alight-emitting layer containing an organic compound.

In general, an organic electroluminescent device (hereinafter referredto as organic EL device) includes a light-emitting layer and a pair ofcounter electrodes interposing the light-emitting layer therebetween inits simplest structure. That is, the organic EL device uses thephenomenon that, when an electric field is applied between both theelectrodes, electrons are injected from a cathode and holes are injectedfrom an anode, and each electron and each hole recombine in thelight-emitting layer to emit light.

In recent years, progress has been made in developing an organic ELdevice using an organic thin film. In order to enhance luminous efficacyparticularly, the optimization of the kind of electrodes has beenattempted for the purpose of improving the efficiency of injection ofcarriers from the electrodes. As a result, there has been developed adevice in which a hole-transporting layer formed of an aromatic diamineand a light-emitting layer formed of an 8-hydroxyquinoline aluminumcomplex (Alq₃) are formed between electrodes as thin films, resulting ina significant improvement in luminous efficacy, as compared torelated-art devices in which a single crystal of anthracene or the likeis used. Thus, the development of the above-mentioned organic EL devicehas been promoted in order to accomplish its practical application to ahigh-performance flat panel having features such as self-luminescenceand rapid response.

Further, investigations have been made on using phosphorescent lightrather than fluorescent light as an attempt to raise the luminousefficacy of a device. Many kinds of devices including theabove-mentioned device in which a hole-transporting layer formed of anaromatic diamine and a light-emitting layer formed of Alg₃ are formedemit light by using fluorescent light emission. However, by usingphosphorescent light emission, that is, by using light emission from atriplet excited state, luminous efficacy is expected to be improved byfrom about three times to about four times, as compared to the case ofusing related-art devices in which fluorescent light (singlet) is used.In order to accomplish this purpose, investigations have been made onadopting a coumarin derivative or a benzophenone derivative as alight-emitting layer, but extremely low luminance has only beenprovided. Further, investigations have been made on using a europiumcomplex as an attempt to use a triplet state, but highly efficient lightemission has not been accomplished. In recent years, many investigationshave been made mainly on an organic metal complex, such as an iridiumcomplex, as described in Patent Literature 1, for the purpose ofattaining high luminous efficacy and a long lifetime.

CITATION LIST Patent Literature

-   [PTL 1] WO 01/041512 A1-   [PTL 2] JP 2001-313178 A-   [PTL 3] JP 2005-162709 A-   [PTL 4] JP 2005-166574 A-   [PTL 5] US 2012/0319088 A1-   [PTL 6] WO 2013/094834 A1

Non Patent Literature

-   [NPL 1] J. Am. Chem. Soc. 2012, 134, 17982-17990-   [NPL 2] J. Am. Chem. Soc. 2010, 132, 6578-6587

In order to obtain high luminous efficacy, host materials that are usedwith the dopant materials described above play an important role. Atypical example of the host materials proposed is4,4′-bis(9-carbazolyl)biphenyl (CBP) as a carbazole compound disclosedin Patent Literature 2. When CBP is used as a host material for a greenphosphorescent light-emitting material typified by atris(2-phenylpyridine)iridium complex (Ir(ppy)₃), the injection balancebetween charges is disturbed because CBP has the characteristic offacilitating the delivery of holes and not facilitating the delivery ofelectrons. Thus, excessively delivered holes flow out into anelectron-transporting layer side, with the result that the luminousefficacy from Ir(ppy)₃ lowers.

In order to provide high luminous efficacy to an organic EL device asdescribed above, it is necessary to use a host material that has hightriplet excitation energy, and is striking a good balance in both charge(hole and electron)-injecting/transporting property. Further desired isa compound that is electrochemically stable and has high heat resistanceand excellent amorphous stability, and hence further improvement hasbeen demanded.

In Patent Literatures 3, 4, 5, and 6 and Non Patent Literatures 1 and 2,there are disclosures of such carborane compounds as shown below.

However, none of the literatures teaches the usefulness of a carboranecompound in which one or more dibenzofuranyl groups are bonded.

SUMMARY OF INVENTION

In order to apply an organic EL device to a display device in a flatpanel display or the like, it is necessary to improve the luminousefficacy of the device and also to ensure sufficiently the stability indriving the device. The present invention has an object to provide, inview of the above-mentioned circumstances, an organic EL device that hashigh efficiency and high driving stability and is practically useful anda compound suitable for the organic EL device.

The inventors of the present invention have made intensiveinvestigations and have consequently found that, when a carboranecompound in which at least one dibenzofuranyl group is bonded is used inan organic EL device, the organic EL device exhibits excellentcharacteristics. As a result, the present invention has been completed.

The present invention relates to a material for an organicelectroluminescent device, including a carborane compound represented bythe following general formula (1).

In the general formula (1):

a ring A represents a divalent carborane group C₂B₁₀H₁₀ represented bythe formula (1a) or the formula (1b), and when the plurality of rings Aare present in a molecule thereof, the rings may be identical to ordifferent from each other;

s represents a number of repetitions and represents an integer of from 1to 4, and n and m each represent a substitution number, n represents aninteger of from 0 to 4 and m represents an integer of from 0 to 4,provided that when n=1, s=1;

L¹ represents an n+1-valent substituted or unsubstituted aromatichydrocarbon group having 6 to 30 carbon atoms, an n+1-valent substitutedor unsubstituted aromatic heterocyclic group having 3 to 30 carbonatoms, or an n+1-valent linked aromatic group formed by linking 2 to 6aromatic rings of the aromatic hydrocarbon group or the aromaticheterocyclic group, and when n=1, L¹ represents a group containing atleast one aromatic heterocyclic group or a single bond;

L² represents a single bond, a divalent substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 carbon atoms, a divalentsubstituted or unsubstituted aromatic heterocyclic group having 3 to 30carbon atoms, or a divalent linked aromatic group formed by linking 2 to6 aromatic rings of the aromatic hydrocarbon group or the aromaticheterocyclic group, and terminal L²-H may be an alkyl group having 1 to12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or anacetyl group;

R represents an alkyl group having 1 to 12 carbon atoms, an alkoxy grouphaving 1 to 12 carbon atoms, an acetyl group, a substituted orunsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, asubstituted or unsubstituted aromatic heterocyclic group having 3 to 30carbon atoms, or a linked aromatic group formed by linking 2 to 6aromatic rings of the aromatic hydrocarbon group or the aromaticheterocyclic group;

when L¹, L², or R represents a linked aromatic group, the group may belinear or branched, and the aromatic rings to be linked may be identicalto or different from each other; and

when a plurality of s's, L²'s, or R's are present in the molecule, theplurality of s's, L²'s, or R's may be identical to or different fromeach other.

In the general formula (1), it is preferred that any one or more of thefollowing (1) to (4) be satisfied:

(1) n represents an integer of 0 or 1;(2) the ring A represents a divalent carborane group C₂B₁₀H₁₀represented by the formula (1a);(3) L¹ and L² each independently represent a substituted orunsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, asubstituted or unsubstituted aromatic heterocyclic group having 3 to 17carbon atoms, or a linked aromatic group formed by linking 2 to 6aromatic rings selected from the aromatic hydrocarbon group and thearomatic heterocyclic group;(4) L¹ and L² each independently represent a substituted orunsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms,or a linked aromatic group formed by linking 2 to 6 aromatic ringsselected from the aromatic heterocyclic group.

Part or the entirety of hydrogen atoms in the carborane compoundrepresented by the general formula (1) may each be substituted withdeuterium.

The present invention also relates to an organic electroluminescentdevice having a structure in which an anode, an organic layer, and acathode are laminated on a substrate, in which the organic layerincludes an organic layer containing the above-mentioned material for anorganic electroluminescent device.

It is preferred that the organic layer containing the material for anorganic electroluminescent device include at least one layer selectedfrom the group consisting of a light-emitting layer, anelectron-transporting layer, and a hole-blocking layer, or include alight-emitting layer containing a phosphorescent light-emitting dopant.When the phosphorescent light-emitting dopant is contained, it ispreferred that its emission wavelength have an emission maximumwavelength at 550 nm or less.

A material for a phosphorescent device of the present invention has astructure in which at least one dibenzofuranyl group is bonded onto acarborane skeleton. A carborane compound having such structural featureenables high-level control of the electron-injecting/transportingproperties because its lowest unoccupied molecular orbital (LUMO) thataffects the electron-injecting/transporting properties is widelydistributed in the entirety of a molecule thereof. Further, the compoundenables efficient light emission from a dopant because that its tripletexcitation energy (T1 energy) is enough high to confine the T1 energy ofthe dopant. By virtue of the foregoing features, the organic EL devicewhich contains the compound can achieve low voltage and high luminousefficacy respectively.

In addition, the material for an organic electroluminescent device ofthe present invention shows a satisfactory amorphous characteristic andhigh heat stability, and at the same time, is extremely stable in anexcited state. Accordingly, an organic EL device using the material hasa long driving lifetime and durability at a practical level.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view for illustrating an example of the structureof an organic EL device.

FIG. 2 is an NMR chart of a carborane compound 1 of the presentinvention.

DESCRIPTION OF EMBODIMENTS

A material for an organic electroluminescent device of the presentinvention is a carborane compound represented by the general formula(1). The carborane compound exhibits such excellent effects as describedabove probably because the compound has a structure in which at leastone dibenzofuranyl group is bonded.

L¹ represents an n+1-valent substituted or unsubstituted aromatichydrocarbon group having 6 to 30 carbon atoms, an n+1-valent substitutedor unsubstituted aromatic heterocyclic group having 3 to 30 carbonatoms, or an n+1-valent linked aromatic group formed by linking 2 to 6aromatic rings of the aromatic hydrocarbon group or the aromaticheterocyclic group. When L¹ represents the linked aromatic group, thegroup may be linear or branched, and the aromatic rings to be linked maybe identical to or different from each other. The same holds true forthe case where L² or R represents a linked aromatic group.

L² represents a single bond, a divalent substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 carbon atoms, a divalentsubstituted or unsubstituted aromatic heterocyclic group having 3 to 30carbon atoms, or a divalent linked aromatic group formed by linking 2 to6 aromatic rings of the aromatic hydrocarbon group or the aromaticheterocyclic group, and terminal L²-H may be an alkyl group having 1 to12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or anacetyl group.

R represents an alkyl group having 1 to 12 carbon atoms, an alkoxy grouphaving 1 to 12 carbon atoms, an acetyl group, a substituted orunsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, asubstituted or unsubstituted aromatic heterocyclic group having 3 to 30carbon atoms, or a linked aromatic group formed by linking 2 to 6aromatic rings of the aromatic hydrocarbon group or the aromaticheterocyclic group.

The case where L¹, L², and R each represent an aromatic hydrocarbongroup, an aromatic heterocyclic group, or a linked aromatic group isdescribed. It should be noted that when L¹, L², and R each represent anysuch group, L¹ represents an nil-valent group, L² represents a divalentgroup, and R represents a monovalent group.

Specific examples of the unsubstituted aromatic hydrocarbon groupinclude groups each produced by removing a hydrogen atom from anaromatic hydrocarbon compound, such as benzene, naphthalene, fluorene,anthracene, phenanthrene, triphenylene, tetraphenylene, fluoranthene,pyrene, or chrysene. Of those, a group produced by removing a hydrogenatom from benzene, naphthalene, fluorene, phenanthrene, or triphenyleneis preferred.

Specific examples of the unsubstituted aromatic heterocyclic groupinclude linking groups each produced by removing a hydrogen atom from anaromatic heterocyclic compound, such as pyridine, pyrimidine, triazine,quinoline, isoquinoline, quinoxaline, naphthyridine, carbazole,dibenzofuran, acridine, azepine, tribenzazepine, phenazine, phenoxazine,phenothiazine, dibenzophosphole, or dibenzoborole. Of those, a groupproduced by removing a hydrogen atom from pyridine, pyrimidine,triazine, carbazole, or dibenzofuran is preferred.

A group produced by removing a hydrogen atom from an aromatic compoundin which a plurality of aromatic hydrocarbon compounds or aromaticheterocyclic compounds are linked to each other is referred to as“linked aromatic group.” The linked aromatic group is a group formed bylinking 2 to 6 aromatic rings, the aromatic rings to be linked may beidentical to or different from each other, and both an aromatichydrocarbon group and an aromatic heterocyclic group may be included.The number of the aromatic rings to be linked is preferably from 2 to 4,more preferably 2 or 3.

Specific examples of the linked aromatic group include groups eachproduced by removing a hydrogen atom from biphenyl, terphenyl,phenylnaphthalene, diphenylnaphthalene, phenylanthracene,diphenylanthracene, diphenylfluorene, bipyridine, bipyrimidine,bitriazine, biscarbazole, bisdibenzofuran, bisdibenzothiophene,phenylpyridine, phenylpyrimidine, phenyltriazine, phenylcarbazole,phenyldibenzofuran, diphenylpyridine, diphenyltriazine,bis(carbazolyl)benzene, bis(dibenzofuranyl)benzene, or the like.

The aromatic hydrocarbon group, the aromatic heterocyclic group, or thelinked aromatic group may have a substituent, and when any such grouphas a substituent, a preferred substituent is an alkyl group having 1 to12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or anacetyl group. A more preferred substituent is an alkyl group having 1 to4 carbon atoms, an alkoxy group having 1 or 2 carbon atoms, or an acetylgroup.

Here, when the linked aromatic group is a divalent group, the group isrepresented by, for example, any one of the following formulae, and itsaromatic rings may be linked in a linear manner or a branched manner.

(Ar¹ to Ar⁶ each represent a substituted or unsubstituted aromatichydrocarbon ring or aromatic heterocycle.)

In the general formula (1), s represents a number of repetitions andrepresents an integer of from 1 to 4, preferably an integer of 1 or 2.

In the general formula (1), m and n each represent a substitutionnumber, n represents an integer of from 0 to 4, and m represents aninteger of from 1 to 4. It is preferred that n represent an integer of 0or 1 and m represent an integer of 1 or 2.

The case where R and terminal L²-H each represent an alkyl group or analkoxy group is described.

The alkyl group may be saturated or unsaturated, and may be linear,branched, or cyclic. Preferred specific examples thereof include: alkylgroups each having 1 to 8 carbon atoms, such as a methyl group, an ethylgroup, an ethenyl group, a propyl group, a propenyl group, an isopropylgroup, a butyl group, a t-butyl group, a pentyl group, a hexyl group,and an octyl group; and cycloalkyl groups each having 5 to 8 carbonatoms, such as a cyclopentyl group and a cyclohexyl group.

The alkoxy group may be linear or branched. Preferred specific examplesthereof include alkoxy groups each having 1 to 8 carbon atoms, such as amethoxy group, an ethoxy group, a propoxy group, an isopropoxy group, abutoxy group, a t-butoxy group, a pentoxy group, a 2-ethylbutoxy group,a hexyloxy group, and an octyloxy group.

In the general formula (1), a ring A represents a divalent carboranegroup C₂B₁₀H₁₀ represented by the formula (1a) or (1b). The two bondinghands of the divalent carborane group may each be produced from C or mayeach be produced from B, but a bonding hand to be bonded to L¹ or L² ispreferably produced from C. Of the divalent carborane groups, acarborane group represented by the formula (1a) is preferred.

The carborane compound represented by the general formula (1) can besynthesized from raw materials selected in accordance with the structureof the target compound by using a known approach.

(A-1) can be synthesized through the following reaction formula withreference to a synthesis example described in Journal of OrganometallicChemistry, 1993, 462, p 19-29.

Specific examples of the carborane compound represented by the generalformula (1) are shown below. However, the material for an organicelectroluminescent device of the present invention is not limitedthereto.

When the material for an organic electroluminescent device of thepresent invention (sometimes referred to as compound of the presentinvention, compound represented by the general formula (1), or carboranecompound) is contained in at least one of a plurality of organic layersof an organic EL device having a structure in which an anode, theplurality of organic layers, and a cathode are laminated on a substrate,an excellent organic electroluminescent device is provided. Alight-emitting layer, an electron-transporting layer, or a hole-blockinglayer is suitable as the organic layer in which the compound of thepresent invention is contained. Here, when the compound of the presentinvention is used in the light-emitting layer, the compound can be usedas a host material for the light-emitting layer containing a fluorescentlight-emitting, delayed fluorescent light-emitting, or phosphorescentlight-emitting dopant. In addition, the compound of the presentinvention can be used as an organic light-emitting material thatradiates fluorescence and delayed fluorescence. When the compound of thepresent invention is used as an organic light-emitting material thatradiates fluorescence and delayed fluorescence, any other organiccompound having a value for at least one of excited singlet energy orexcited triplet energy higher than that of the compound is preferablyused as the host material. The compound of the present invention isparticularly preferably incorporated as a host material for thelight-emitting layer containing the phosphorescent light-emittingdopant.

Next, an organic EL device using the material for an organicelectroluminescent device of the present invention is described.

The organic EL device of the present invention includes organic layersincluding at least one light-emitting layer between an anode and acathode laminated on a substrate. In addition, at least one of theorganic layers contains the material for an organic electroluminescentdevice of the present invention. The material for an organicelectroluminescent device of the present invention is advantageouslycontained in the light-emitting layer together with a phosphorescentlight-emitting dopant.

Next, the structure of the organic EL device of the present invention isdescribed with reference to the drawings. However, the structure of theorganic EL device of the present invention is by no means limited to oneillustrated in the drawings.

FIG. 1 is a sectional view for illustrating an example of the structureof a general organic EL device used in the present invention. Referencenumeral 1 represents a substrate, reference numeral 2 represents ananode, reference numeral 3 represents a hole-injecting layer, referencenumeral 4 represents a hole-transporting layer, reference numeral 5represents a light-emitting layer, reference numeral 6 represents anelectron-transporting layer, and reference numeral 7 represents acathode. The organic EL device of the present invention may include anexciton-blocking layer adjacent to the light-emitting layer, or mayinclude an electron-blocking layer between the light-emitting layer andthe hole-injecting layer. The exciton-blocking layer may be inserted onany of the anode side and the cathode side of the light-emitting layer,and may also be inserted simultaneously on both sides. The organic ELdevice of the present invention includes the substrate, the anode, thelight-emitting layer, and the cathode as its essential layers. Theorganic EL device of the present invention preferably includes ahole-injecting/transporting layer and an electron-injecting/transportinglayer in addition to the essential layers, and more preferably includesa hole-blocking layer between the light-emitting layer and theelectron-injecting/transporting layer. It should be noted that thehole-injecting/transporting layer means any one or both of thehole-injecting layer and the hole-transporting layer, and that theelectron-injecting/transporting layer means any one or both of anelectron-injecting layer and the electron-transporting layer.

It should be noted that it is possible to adopt a reverse structure ascompared to FIG. 1, that is, the reverse structure being formed bylaminating the layers on the substrate 1 in the order of the cathode 7,the electron-transporting layer 6, the light-emitting layer 5, thehole-transporting layer 4, and the anode 2. In this case as well, somelayers may be added or eliminated as required.

—Substrate—

The organic EL device of the present invention is preferably supportedby a substrate. The substrate is not particularly limited, and anysubstrate that has long been conventionally used for an organic ELdevice may be used. For example, a substrate made of glass, atransparent plastic, quartz, or the like may be used.

—Anode—

Preferably used as the anode in the organic EL device is an anode formedby using, as an electrode substance, any of a metal, an alloy, anelectrically conductive compound, and a mixture thereof, all of whichhave a large work function (4 eV or more). Specific examples of suchelectrode substance include metals such as Au and conductive transparentmaterials such as CuI, indium tin oxide (ITO), SnO₂, and ZnO. Inaddition, a material such as IDIXO (In₂O₃—ZnO), which can produce anamorphous, transparent conductive film, may be used. In order to producethe anode, it may be possible to form any of those electrode substancesinto a thin film by using a method such as vapor deposition orsputtering and form a pattern having a desired shape thereon byphotolithography. Alternatively, in the case of not requiring highpattern accuracy (about 100 μm or more), a pattern may be formed via amask having a desired shape when any of the above-mentioned electrodesubstances is subjected to vapor deposition or sputtering.Alternatively, when a coatable substance, such as an organic conductivecompound, is used, a wet film-forming method, such as a printing methodor a coating method, may be used. When luminescence is taken out fromthe anode, the transmittance of the anode is desirably controlled tomore than 10%. In addition, the sheet resistance of the anode ispreferably several hundred ohms per square (Ω/□) or less. Further, thethickness of the film is, depending on its material, selected from therange of generally from 10 nm to 1,000 nm, preferably from 10 nm to 200nm.

—Cathode—

On the other hand, used as the cathode is a cathode formed by using, asan electrode substance, any of a metal (referred to aselectron-injecting metal), an alloy, an electrically conductivecompound, and a mixture thereof, all of which have a small work function(4 eV or less). Specific examples of such electrode substance includesodium, a sodium-potassium alloy, magnesium, lithium, a magnesium/coppermixture, a magnesium/silver mixture, a magnesium/aluminum mixture, amagnesium/indium mixture, an aluminum/aluminum oxide (Al₂O₃) mixture,indium, a lithium/aluminum mixture, and a rare earth metal. Of those,for example, a mixture of an electron-injecting metal and a secondmetal, which is a stable metal having a larger work function value thanthe former metal, such as a magnesium/silver mixture, amagnesium/aluminum mixture, a magnesium/indium mixture, analuminum/aluminum oxide (Al₂O₃) mixture, or a lithium/aluminum mixture,or aluminum, is suitable from the viewpoints of an electron-injectingproperty and durability against oxidation or the like. The cathode canbe produced by forming any of those electrode substances into a thinfilm by using a method such as vapor deposition or sputtering. Inaddition, the sheet resistance of the cathode is preferably severalhundred Ω/□ or less, and the thickness of the film is selected from therange of generally from 10 nm to 5 μm, preferably from 50 nm to 200 nm.It should be noted that, in order for luminescence produced to passthrough, any one of the anode and cathode of the organic EL device ispreferably transparent or semi-transparent, because the light emissionluminance improves.

In addition, after the above-mentioned metal has been formed into a filmhaving a thickness of from 1 nm to 20 nm as a cathode, the conductivetransparent material mentioned in the description of the anode is formedinto a film on the cathode, thereby being able to produce a transparentor semi-transparent cathode. Through the application of this, a devicein which both the anode and cathode have transparency can be produced.

—Light-Emitting Layer—

The light-emitting layer is a layer that emits light after theproduction of an exciton by the recombination of a hole injected fromthe anode and an electron injected from the cathode, and thelight-emitting layer contains an organic light-emitting material and ahost material.

When the light-emitting layer is a fluorescent light-emitting layer, atleast one kind of fluorescent light-emitting material may be used aloneas the fluorescent light-emitting material. However, it is preferredthat the fluorescent light-emitting material be used as a fluorescentlight-emitting dopant and the host material be contained.

The carborane compound represented by the general formula (1) can beused as the fluorescent light-emitting material in the light-emittinglayer. However, the fluorescent light-emitting material is knownthrough, for example, many patent literatures, and hence can be selectedtherefrom. Examples thereof include a benzoxazole derivative, abenzothiazole derivative, a benzimidazole derivative, a styrylbenzenederivative, a polyphenyl derivative, a diphenylbutadiene derivative, atetraphenylbutadiene derivative, a naphthalimide derivative, a coumarinderivative, a fused aromatic compound, a perinone derivative, anoxadiazole derivative, an oxazine derivative, an aldazine derivative, apyrrolidine derivative, a cyclopentadiene derivative, abisstyrylanthracene derivative, a quinacridone derivative, apyrrolopyridine derivative, a thiadiazolopyridine derivative, astyrylamine derivative, a diketopyrrolopyrrole derivative, an aromaticdimethylidene compound, various metal complexes typified by a metalcomplex of a 8-quinolinol derivative, and a metal complex, rare earthcomplex, or transition metal complex of a pyrromethene derivative,polymer compounds such as polythiophene, polyphenylene, andpolyphenylene vinylene, and an organic silane derivative. Of those, forexample, the following compound is preferred: a fused aromatic compound,a styryl compound, a diketopyrrolopyrrole compound, an oxazine compound,or a pyrromethene metal complex, transition metal complex, or lanthanoidcomplex. For example, the following compound is more preferrednaphthacene, pyrene, chrysene, triphenylene, benzo[c]phenanthrene,benzo[a]anthracene, pentacene, perylene, fluoranthene,acenaphthofluoranthene, dibenzo[a,j]anthracene, dibenzo[a,h]anthracene,benzo[a]naphthacene, hexacene, anthanthrene, naphtho[2,1-f]isoquinoline,α-naphthaphenanthridine, phenanthroxazole, quinolino[6,5-f]quinoline, orbenzothiophanthrene. Those compounds may each have an alkyl group, arylgroup, aromatic heterocyclic group, or diarylamino group as asubstituent.

The carborane compound represented by the general formula (1) can beused as a fluorescent host material in the light-emitting layer.However, the fluorescent host material is known through, for example,many patent literatures, and hence can be selected therefrom. Forexample, the following material can be used: a compound having a fusedaryl ring, such as naphthalene, anthracene, phenanthrene, pyrene,chrysene, naphthacene, triphenylene, perylene, fluoranthene, fluorene,or indene, or a derivative thereof; an aromatic amine derivative, suchas N,N′-dinaphthyl-N,N′-diphenyl-4,4′-diphenyl-1,1′-diamine; a metalchelated oxinoid compound typified by tris(8-quinolinato)aluminum(III);a bisstyryl derivative, such as a distyrylbenzene derivative; atetraphenylbutadiene derivative; an indene derivative; a coumarinderivative; an oxadiazole derivative; a pyrrolopyridine derivative; aperinone derivative; a cyclopentadiene derivative; a pyrrolopyrrolederivative; a thiadiazolopyridine derivative; a dibenzofuran derivative;a carbazole derivative; an indolocarbazole derivative; a triazinederivative; or a polymer-based derivative, such as a polyphenylenevinylene derivative, a poly-p-phenylene derivative, a polyfluorenederivative, a polyvinyl carbazole derivative, or a polythiophenederivative. However, the fluorescent host material is not particularlylimited thereto.

When the fluorescent light-emitting material is used as a fluorescentlight-emitting dopant and the host material is contained, the content ofthe fluorescent light-emitting dopant in the light-emitting layerdesirably falls within the range of from 0.01 wt % to 20 wt %,preferably from 0.1 wt % to 10 wt %.

An organic EL device typically injects charges from both of itselectrodes, i.e., its anode and cathode into a light-emitting substanceto produce a light-emitting substance in an excited state, and causesthe substance to emit light. In the case of a charge injection-typeorganic EL device, it is said that 25% of the produced excitons areexcited to a singlet excited state and the remaining 75% of the excitonsare excited to a triplet excited state. As described in AdvancedMaterials 2009, 21, 4802-4806, it has been known that after a specificfluorescent light-emitting substance has undergone an energy transitionto a triplet excited state as a result of intersystem crossing or thelike, the substance is subjected to inverse intersystem crossing to asinglet excited state by triplet-triplet annihilation or the absorptionof thermal energy to radiate fluorescence, thereby expressing thermallyactivated delayed fluorescence. The organic EL device of the presentinvention can also express delayed fluorescence. In this case, the lightemission can include both fluorescent light emission and delayedfluorescent light emission. It should be noted that light emission fromthe host material may be present in part of the light emission.

When the light-emitting layer is a delayed fluorescent light-emittinglayer, at least one kind of delayed fluorescent light-emitting materialmay be used alone as a delayed fluorescent light-emitting material.However, it is preferred that the delayed fluorescent light-emittingmaterial be used as a delayed fluorescent light-emitting dopant and thehost material be contained.

Although the carborane compound represented by the general formula (1)can be used as the delayed fluorescent light-emitting material in thelight-emitting layer, a material selected from known delayed fluorescentlight-emitting materials can also be used. Examples thereof include atin complex, an indolocarbazole derivative, a copper complex, and acarbazole derivative. Specific examples thereof include, but not limitedto, compounds described in the following non patent literatures andpatent literature.

(1) Adv. Mater. 2009, 21, 4802-4806, (2) Appl. Phys. Lett. 98, 083302(2011), (3) JP 2011-213643 A, and (4) J. Am. Chem. Soc. 2012, 134,14706-14709.

Specific examples of the delayed fluorescent light-emitting material areshown below, but the delayed fluorescent light-emitting material is notlimited to the following compounds.

When the delayed fluorescent light-emitting material is used as adelayed fluorescent light-emitting dopant and the host material iscontained, the content of the delayed fluorescent light-emitting dopantin the light-emitting layer desirably falls within the range of from0.01 wt % to 50 wt %, preferably from 0.1 wt % to 20 wt %, morepreferably from 0.01 wt % to 10%.

The carborane compound represented by the general formula (1) can beused as the delayed fluorescent host material in the light-emittinglayer. However, the delayed fluorescent host material can also beselected from compounds except the carborane. For example, the followingcompound can be used: a compound having a fused aryl ring, such asnaphthalene, anthracene, phenanthrene, pyrene, chrysene, naphthacene,triphenylene, perylene, fluoranthene, fluorene, or indene, or aderivative thereof; an aromatic amine derivative, such asN,N′-dinaphthyl-N,N′-diphenyl-4,4′-diphenyl-1,1′-diamine; a metalchelated oxinoid compound typified by tris(8-quinolinato)aluminum(III);a bisstyryl derivative, such as a distyrylbenzene derivative; atetraphenylbutadiene derivative; an indene derivative; a coumarinderivative; an oxadiazole derivative; a pyrrolopyridine derivative; aperinone derivative; a cyclopentadiene derivative; a pyrrolopyrrolederivative; a thiadiazolopyridine derivative; a dibenzofuran derivative;a carbazole derivative; an indolocarbazole derivative; a triazinederivative; or a polymer-based derivative, such as a polyphenylenevinylene derivative, a poly-p-phenylene derivative, a polyfluorenederivative, a polyvinyl carbazole derivative, a polythiophenederivative, or an arylsilane derivative. However, the delayedfluorescent host material is not particularly limited thereto.

When the light-emitting layer is a phosphorescent light-emitting layer,the light-emitting layer contains a phosphorescent light-emitting dopantand a host material. It is recommended to use, as a material for thephosphorescent light-emitting dopant, a material containing an organicmetal complex including at least one metal selected from ruthenium,rhodium, palladium, silver, rhenium, osmium, iridium, platinum, andgold.

Preferred examples of the phosphorescent light-emitting dopant includecomplexes such as Ir(ppy)₃, complexes such as Ir(bt)₂.acac₃, andcomplexes such as PtOEt₃, the complexes each having a noble metalelement, such as Ir, as a central metal. Specific examples of thosecomplexes are shown below, but the complexes are not limited to thecompounds described below.

It is desired that the content of the phosphorescent light-emittingdopant in the light-emitting layer fall within the range of from 2 wt %to 40 wt %, preferably from 5 wt % to 30 wt %.

When the light-emitting layer is a phosphorescent light-emitting layer,it is preferred to use, as a host material in the light-emitting layer,the carborane compound of the present invention. However, when thecarborane compound is used in any other organic layer except thelight-emitting layer, the material to be used in the light-emittinglayer may be another host material except the carborane compound, or thecarborane compound and any other host material may be used incombination. Further, a plurality of kinds of known host materials maybe used in combination.

It is preferred to use, as a usable known host compound, a compound thathas a hole-transporting ability or an electron-transporting ability, iscapable of preventing luminescence from having a longer wavelength, andhas a high glass transition temperature.

Any such other host material is known through, for example, many patentliteratures, and hence can be selected therefrom. Specific examples ofthe host material include, but are not particularly limited to, anindole derivative, a carbazole derivative, a triazole derivative, anoxazole derivative, an oxadiazole derivative, an imidazole derivative, apolyarylalkane derivative, a pyrazoline derivative, a pyrazolonederivative, a phenylenediamine derivative, an arylamine derivative, anamino-substituted chalcone derivative, a styrylanthracene derivative, afluorenone derivative, a hydrazone derivative, a stilbene derivative, asilazane derivative, an aromatic tertiary amine compound, a styrylaminecompound, an aromatic dimethylidene-based compound, a porphyrin-basedcompound, an anthraquinodimethane derivative, an anthrone derivative, adiphenylquinone derivative, a thiopyran dioxide derivative, aheterocyclic tetracarboxylic acid anhydride, such as naphthaleneperylene, a phthalocyanine derivative, various metal complexes typifiedby a metal complex of an 8-quinolinol derivative, a metalphthalocyanine, and metal complexes of benzoxazole and benzothiazolederivatives, and polymer compounds, such as a polysilane-based compound,a poly(N-vinylcarbazole) derivative, an aniline-based copolymer, athiophene oligomer, a polythiophene derivative, a polyphenylenederivative, a polyphenylenevinylene derivative, and a polyfluorenederivative.

The light-emitting layer, which may be any one of a fluorescentlight-emitting layer, a delayed fluorescent light-emitting layer, and aphosphorescent light-emitting layer, is preferably the phosphorescentlight-emitting layer.

—Injecting Layer—

The injecting layer refers to a layer formed between an electrode and anorganic layer for the purposes of lowering a driving voltage andimproving light emission luminance, and includes a hole-injecting layerand an electron-injecting layer. The injecting layer may be interposedbetween the anode and the light-emitting layer or the hole-transportinglayer, or may be interposed between the cathode and the light-emittinglayer or the electron-transporting layer. The injecting layer may beformed as required.

—Hole-Blocking Layer—

The hole-blocking layer has, in a broad sense, the function of anelectron-transporting layer, and is formed of a hole-blocking materialthat has a remarkably small ability to transport holes while having afunction of transporting electrons, and hence the hole-blocking layer iscapable of improving the probability of recombining an electron and ahole by blocking holes while transporting electrons.

It is preferred to use the carborane compound represented by the generalformula (1) according to the present invention for the hole-blockinglayer. However, when the carborane compound is used in any other organiclayer, a known material for a hole-blocking layer may be used. Inaddition, a material for the electron-transporting layer to be describedlater can be used as a material for the hole-blocking layer as required.

—Electron-Blocking Layer—

The electron-blocking layer is formed of a material that has aremarkably small ability to transport electrons while having a functionof transporting holes, and hence the electron-blocking layer is capableof improving the probability of recombining an electron and a hole byblocking electrons while transporting holes.

A material for the hole-transporting layer to be described later can beused as a material for the electron-blocking layer as required. Thethickness of the electron-blocking layer is preferably from 3 nm to 100nm, more preferably from 5 nm to 30 nm.

—Exciton-Blocking Layer—

The exciton-blocking layer refers to a layer for blocking excitonsproduced by the recombination of a hole and an electron in thelight-emitting layer from diffusing into charge-transporting layers. Theinsertion of this layer enables efficient confinement of the excitons inthe light-emitting layer, thereby being able to improve the luminousefficacy of the device. The exciton-blocking layer can be inserted onany of the anode side and the cathode side of the adjacentlight-emitting layer, and can also be inserted simultaneously on bothsides.

Although the carborane compound represented by the general formula (1)can be used as a material for the exciton-blocking layer, as othermaterials therefor, there are given, for example,1,3-dicarbazolylbenzene (mCP) andbis(2-methyl-8-quinolinolato)-4-phenylphenolatoaluminum(III) (BAlq).

—Hole-Transporting Layer—

The hole-transporting layer is formed of a hole-transporting materialhaving a function of transporting holes, and a single hole-transportinglayer or a plurality of hole-transporting layers can be formed.

The hole-transporting material has a hole-injecting property or ahole-transporting property or has an electron-blocking property, and anyof an organic material and an inorganic material can be used as thehole-transporting material. Although it is preferred to use thecarborane compound represented by the general formula (1) as a knownhole-transporting material that can be used, any compound selected fromconventionally known compounds can be used. Examples of the knownhole-transporting material that can be used include a triazolederivative, an oxadiazole derivative an imidazole derivative, apolyarylalkane derivative, a pyrazoline derivative, and a pyrazolonederivative, a phenylenediamine derivative, an arylamine derivative, anamino-substituted chalcone derivative, an oxazole derivative, astyrylanthracene derivative, a fluorenone derivative, a hydrazonederivative, a stilbene derivative, a silazane derivative, ananiline-based copolymer, and a conductive high-molecular weightoligomer, in particular, a thiophene oligomer. However, a porphyrincompound, an aromatic tertiary amine compound, or a styrylamine compoundis preferably used, and an aromatic tertiary amine compound is morepreferably used.

—Electron-Transporting Layer—

The electron-transporting layer is formed of a material having afunction of transporting electrons, and a single electron-transportinglayer or a plurality of electron-transporting layers can be formed.

An electron-transporting material (which also serves as a hole-blockingmaterial in some cases) only needs to have a function of transferringelectrons injected from the cathode into the light-emitting layer.Although it is preferred to use the carborane compound of the presentinvention for the electron-transporting layer, any compound selectedfrom conventionally known compounds can be used. Examples thereofinclude a nitro-substituted fluorene derivative, a diphenylquinonederivative, a thiopyran dioxide derivative, a carbodiimide, afluorenylidenemethane derivative, anthraquinodimethane, an anthronederivative, and an oxadiazole derivative. Further, a thiadiazolederivative prepared by substituting an oxygen atom on an oxadiazole ringwith a sulfur atom in the oxadiazole derivative or a quinoxalinederivative that has a quinoxaline ring known as an electron withdrawinggroup can be used as the electron-transporting material. Further, apolymer material in which any such material is introduced in a polymerchain or is used as a polymer main chain can be used.

EXAMPLES

Now, the present invention is described in more detail by way ofExamples. It should be appreciated that the present invention is notlimited to Examples below and can be carried out in various forms aslong as the various forms do not deviate from the gist of the presentinvention.

The route described below was used to synthesize a carborane compound tobe used as a material for an organic electroluminescent device. Itshould be noted that the number of each compound corresponds to thenumber given to the chemical formula.

Example 1

A compound 1 is synthesized in accordance with the following reactionformulae.

Under a nitrogen atmosphere, 35.0 g (0.243 mol) of m-carborane and 350mL of 1,2-dimethoxyethane (DME) were added, and the resultant DMEsolution was cooled to 0° C. 96.8 mL of a 2.69 M solution ofn-butyllithium in hexane was dropped to the solution, and the mixturewas stirred under ice cooling for 30 minutes. 67 mL of pyridine wasadded to the resultant and the mixture was stirred at room temperaturefor 10 minutes. After that, 75.6 g (0.763 mol) of copper(I) chloride wasadded to the resultant and the mixture was stirred at 65° C. for 30minutes. After that, 76.4 g (0.260 mol) of 2-iododibenzofuran was addedto the resultant and the mixture was stirred at 95° C. overnight. Thereaction solution was cooled to room temperature, and then theprecipitated crystal was taken by filtration and the solvent wasdistilled off under reduced pressure. The resultant residue was purifiedby silica gel column chromatography to provide 25.0 g (3.22 mmol, 33%yield) of an intermediate A.

Under a nitrogen atmosphere, 30.0 g (0.07 mol) of2,8-diiododibenzofuran, 11.9 g (0.07 mol) of carbazole, 1.33 g (7.0mmol) of copper iodide, 44.6 g (0.21 mol) of tripotassium phosphate, 2.4g (21.0 mmol) of trans-1,2-cyclohexanediamine, and 1 L of 1,4-dioxanewere added, and the mixture was stirred at 115° C. overnight. Thereaction solution was cooled to room temperature, and then theprecipitated crystal was taken by filtration and the solvent wasdistilled off under reduced pressure. The resultant residue was purifiedby silica gel column chromatography to provide 14.9 g (2.17 mmol, 47%yield) of an intermediate B as a white solid.

Under a nitrogen atmosphere, 8.8 g (0.0285 mol) of the intermediate Aand 63.0 mL of 1,2-dimethoxyethane (DME) were added, and the resultantDME solution was cooled to 0° C. 11.3 mL of a 2.69 M solution ofn-butyllithium in hexane was dropped to the solution, and the mixturewas stirred under ice cooling for 30 minutes. 7.8 mL of pyridine wasadded to the resultant and the mixture was stirred at room temperaturefor 10 minutes. After that, 8.7 g (88.4 mmol) of copper(I) chloride wasadded to the resultant and the mixture was stirred at 65° C. for 30minutes. After that, 14.0 g (0.0305 mol) of the intermediate B was addedto the resultant and the mixture was stirred at 95° C. for 4 days. Thereaction solution was cooled to room temperature, and then theprecipitated crystal was taken by filtration and the solvent wasdistilled off under reduced pressure. The resultant residue was purifiedby silica gel column chromatography to provide 3.0 g (4.67 mmol, 16%yield) of a compound 1. APCI-TOFMS, m/z 642 [M+H]+. The measurementresult of 1H-NMR (measurement solvent: CDCl3) is shown in FIG. 2.

Compounds 13, 25, 26, 29, and 36 were synthesized in conformity with thesynthesis example. In addition, compounds H-1 and H-2 for comparisonwere synthesized.

Example 2

Each thin film was laminated by a vacuum deposition method at a degreeof vacuum of 2.0×10⁻⁵ Pa on a glass substrate on which an anode formedof indium tin oxide (ITO) having a thickness of 70 nm had been formed.First, copper phthalocyanine (CuPC) was formed into a layer having athickness of 30 nm to serve as a hole-injecting layer on the ITO. Next,diphenyl naphthyl diamine (NPD) was formed into a layer having athickness of 15 nm to serve as a hole-transporting layer. Next, thecompound 1 serving as a host material for a light-emitting layer and aniridium complex [iridium(III) bis(4,6-di-fluorophenyl)-pyridinato-N,C2′]picolinate] (FIrpic) serving as ablue phosphorescent material as a dopant were co-deposited fromdifferent deposition sources onto the hole-transporting layer to form alight-emitting layer having a thickness of 30 nm. The concentration ofFIrpic was 20%. Next, Alga was formed into a layer having a thickness of25 nm to serve as an electron-transporting layer. Further, lithiumfluoride (LiF) was formed into a layer having a thickness of 1.0 nm toserve as an electron-injecting layer on the electron-transporting layer.Finally, aluminum (Al) was formed into a layer having a thickness of 70nm to serve as an electrode on the electron-injecting layer. Theresultant organic EL device has such a layer construction that theelectron-injecting layer is added between the cathode and theelectron-transporting layer in the organic EL device illustrated in FIG.1.

An external power source was connected to the resultant organic ELdevice to apply a DC voltage to the device. As a result, it wasconfirmed that the device had such light-emitting characteristics asshown in Table 2. The columns “luminance”, “voltage”, and “luminousefficacy” in Table 1 show values at 2.5 mA/cm² (initialcharacteristics). It should be noted that the maximum wavelength of theemission spectrum of the device was 475 nm, and hence the acquisition oflight emission from FIrpic was found.

Examples 3 to 7

Organic EL devices were each produced in the same manner as in Example 2except that the compound 13, 25, 26, 29, or 36 was used instead of thecompound 1 as the host material for the light-emitting layer in Example2.

Comparative Example 1

An organic EL device was produced in the same manner as in Example 2except that mCP was used as the host material for the light-emittinglayer in Example 2.

Comparative Examples 2 and 3

Organic EL devices were each produced in the same manner as in Example 2except that the compound H-1 or H-2 was used as the host material forthe light-emitting layer in Example 2.

The organic EL devices obtained in Examples 2 to 7 and ComparativeExamples 1 to 3 were evaluated in the same manner as in Example 3. As aresult, it was confirmed that the devices had such light-emittingcharacteristics as shown in Table 1. It should be noted that the maximumwavelength of each of the emission spectra of the organic EL devicesobtained in Examples 2 to 7 and Comparative Examples 1 to 3 was 475 nm,and hence the acquisition of light emission from FIrpic was identified.

TABLE 1 Host Visual luminous material Luminance Voltage efficacycompound (cd/m²) (V) (lm/W) Example 2 1 200 7.3 3.4 Example 3 13 180 7.13.2 Example 4 25 210 7.4 3.6 Example 5 26 210 7.6 3.5 Example 6 29 1907.6 3.1 Example 7 36 200 7.0 3.6 Comparative mCP 140 8.7 2.0 Example 1Comparative H-1 100 7.7 1.6 Example 2 Comparative H-2 140 7.5 2.4Example 3

It is found from Table 1 that Examples 2 to 7 each using the carboranecompound of the present invention in its light-emitting layer showcharacteristics better than those of Comparative Examples 1 to 4 interms of luminous efficacy.

Example 8

Each thin film was laminated by a vacuum deposition method at a degreeof vacuum of 2.0×10⁻⁵ Pa on a glass substrate on which an anode formedof indium tin oxide (ITO) having a thickness of 70 nm had been formed.First, copper phthalocyanine (CuPC) was formed into a layer having athickness of 30 nm to serve as a hole-injecting layer on the ITO. Next,diphenyl naphthyl diamine (NPD) was formed into a layer having athickness of 15 nm to serve as a hole-transporting layer. Next, thecompound 1 serving as a host material for a light-emitting layer andIr(ppy)₃ serving as a dopant were co-deposited from different depositionsources onto the hole-transporting layer to form a light-emitting layerhaving a thickness of 30 nm. The concentration of Ir(ppy)₃ was 10%.Next, Alq₃ was formed into a layer having a thickness of 25 nm to serveas an electron-transporting layer. Further, lithium fluoride (LiF) wasformed into a layer having a thickness of 1 nm to serve as anelectron-injecting layer on the electron-transporting layer. Finally,aluminum (Al) was formed into a layer having a thickness of 70 nm toserve as an electrode on the electron-injecting layer. Thus, an organicEL device was produced.

An external power source was connected to the resultant organic ELdevice to apply a DC voltage to the device. As a result, it wasconfirmed that the device had such light-emitting characteristics asshown in Table 2. The columns “luminance”, “voltage”, and “luminousefficacy” in Table 2 show values at the time of driving at 20 mA/cm²(initial characteristics). The maximum wavelength of the emissionspectrum of the device was 530 nm, and hence the acquisition of lightemission from Ir(ppy)₃ was found.

Examples 9 to 13

Organic EL devices were each produced in the same manner as in Example 7except that the compound 13, 25, 26, 29, or 36 was used instead of thecompound 1 as the host material for the light-emitting layer in Example10.

Comparative Examples 4 to 6

Organic EL devices were each produced in the same manner as in Example 8except that CBP, H-1, or H-2 was used as the host material for thelight-emitting layer in Example 8.

The organic EL devices obtained in Examples and Comparative Examplesabove were evaluated in the same manner as in Example 8. As a result, itwas confirmed that the devices had such light-emitting characteristicsas shown in Table 2. It should be noted that the maximum wavelength ofeach of the emission spectra of the organic EL devices obtained inExamples and Comparative Examples above was 530 nm, and hence theacquisition of light emission from Ir(ppy)₃ was identified.

TABLE 2 Host Visual luminous material Luminance Voltage efficacycompound (cd/m²) (V) (lm/W) Example 8 1 2,000 8.5 3.7 Example 9 13 1,9808.3 3.7 Example 10 25 2,100 8.6 3.8 Example 11 26 2,100 8.7 3.8 Example12 29 1,980 8.7 3.6 Example 13 36 2,000 8.3 3.8 Comparative CBP 1,1208.7 2.0 Example 4 Comparative H-1 1,200 8.5 2.2 Example 5 ComparativeH-2 1,000 8.3 1.9 Example 6

It is found from Table 2 that Examples 8 to 13 each using the carboranecompound of the present invention in its light-emitting layer showcharacteristics better than those of Comparative Examples 4 to 6 interms of luminous efficacy.

Example 14

Each thin film was laminated by a vacuum deposition method at a degreeof vacuum of 2.0×10⁻⁵ Pa on a glass substrate on which an anode formedof indium tin oxide (ITO) having a thickness of 70 nm had been formed.First, copper phthalocyanine (CuPC) was formed into a layer having athickness of 30 nm to serve as a hole-injecting layer on the ITO. Next,diphenyl naphthyl diamine (NPD) was formed into a layer having athickness of 15 nm to serve as a hole-transporting layer. Next, mCPserving as a host material for a light-emitting layer and FIrpic servingas a dopant were co-deposited from different deposition sources onto thehole-transporting layer to form a light-emitting layer having athickness of 30 nm. The concentration of FIrpic was 20 wt %. Next, thecompound 1 was formed into a layer having a thickness of 5 nm to serveas a hole-blocking layer on the light-emitting layer. Next, Alg₃ wasformed into a layer having a thickness of 20 nm to serve as anelectron-transporting layer. Further, lithium fluoride (LiF) was formedinto a layer having a thickness of 1.0 nm to serve as anelectron-injecting layer on the electron-transporting layer. Finally,aluminum (Al) was formed into a layer having a thickness of 70 nm toserve as an electrode on the electron-injecting layer. The resultantorganic EL device has such a layer construction that theelectron-injecting layer is added between the cathode and theelectron-transporting layer and the hole-blocking layer is added betweenthe light-emitting layer and the electron-transporting layer in theorganic EL device illustrated in FIG. 1.

An external power source was connected to the resultant organic ELdevice to apply a DC voltage to the device. As a result, it wasconfirmed that the device had such light-emitting characteristics asshown in Table 3. The columns “luminance”, “voltage”, and “luminousefficacy” in Table 3 show values at the time of driving at 20 mA/cm².The maximum wavelength of the emission spectrum of the device was 475nm, and hence the acquisition of light emission from FIrpic was found.

Examples 15 to 19

Organic EL devices were each produced in the same manner as in Example14 except that the compound 13, 25, 26, 29, or 36 was used instead ofthe compound 1 as the hole-blocking material in Example 14.

Comparative Example 7

An organic EL device was produced in the same manner as in Example 14except that the thickness of Alga serving as the electron-transportinglayer in Example 14 was changed to 25 nm and the hole-blocking layer wasnot formed.

Comparative Examples 8 and 9

An organic EL device was produced in the same manner as in Example 14except that the compound H-1 or H-2 was used as the hole-blockingmaterial in Example 14.

The organic EL devices obtained in Examples and Comparative Examplesabove were evaluated in the same manner as in Example 14. As a result,it was confirmed that the devices had such light-emittingcharacteristics as shown in Table 3. It should be noted that the maximumwavelength of each of the emission spectra of the organic EL devicesobtained in Examples and Comparative Examples above was 475 nm, andhence the acquisition of light emission from FIrpic was identified. Itshould be noted that each of the host materials for the light-emittinglayers used in Examples 15 to 19 and Comparative Examples 7 to 9 is mCP.

TABLE 3 Hole-bloc king Visual luminous material Luminance Voltageefficacy compound (cd/m²) (V) (lm/W) Example 14 1 210 8.0 3.3 Example 1513 190 7.8 3.1 Example 16 25 195 8.0 3.1 Example 17 26 195 8.0 3.1Example 18 29 200 8.0 3.1 Example 19 36 210 7.8 3.4 Comparative — 1408.7 2.0 Example 7 Comparative H-1 170 8.2 2.6 Example 8 Comparative H-2180 8.3 2.7 Example 9

It is found from Table 3 that Examples 14 to 19 each using the carboranecompound of the present invention in its hole-blocking layer showcharacteristics better than those of Comparative Example 7 not using thehole-blocking material and Comparative Examples 8 and 9 each using theother compound.

REFERENCE SIGNS LIST

1 substrate, 2 anode, 3 hole-injecting layer, 4 hole-transporting layer,5 light-emitting layer, 6 electron-transporting layer, 7 cathode

1. A material for an organic electroluminescent device, comprising acarborane compound represented by the general formula (1):

where: a ring A represents a divalent carborane group C₂B₁₀H₁₀represented by the formula (1a) or the formula (1b), and when theplurality of rings A are present in a molecule thereof, the rings may beidentical to or different from each other, s represents a number ofrepetitions and represents an integer of from 1 to 4, and n and m eachrepresent a substitution number, n represents an integer of from 0 to 4and m represents an integer of from 0 to 4, provided that when n=1, srepresents 1; L¹ represents an n+1-valent substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 carbon atoms, an n+1-valentsubstituted or unsubstituted aromatic heterocyclic group having 3 to 30carbon atoms, or an n+1-valent linked aromatic group formed by linking 2to 6 aromatic rings of the aromatic hydrocarbon group or the aromaticheterocyclic group, when L¹ represents the linked aromatic group, thegroup may be linear or branched, and the aromatic rings to be linked maybe identical to or different from each other, and when n=1, L¹represents a group containing at least one aromatic heterocyclic groupor a single bond; L² represents a single bond, a divalent substituted orunsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, adivalent substituted or unsubstituted aromatic heterocyclic group having3 to 30 carbon atoms, or a divalent linked aromatic group formed bylinking 2 to 6 aromatic rings of the aromatic hydrocarbon group or thearomatic heterocyclic group, when L² represents the linked aromaticgroup, the group may be linear or branched, and the aromatic rings to belinked may be identical to or different from each other, and terminalL²-H may be an alkyl group having 1 to 12 carbon atoms, an alkoxy grouphaving 1 to 12 carbon atoms, or an acetyl group; R represents an alkylgroup having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbonatoms, an acetyl group, a substituted or unsubstituted aromatichydrocarbon group having 6 to 30 carbon atoms, a substituted orunsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms,or a linked aromatic group formed by linking 2 to 6 aromatic rings ofthe aromatic hydrocarbon group or the aromatic heterocyclic group, andwhen R represents the linked aromatic group, the group may be linear orbranched, and the aromatic rings to be linked may be identical to ordifferent from each other; and when a plurality of s's, L²'s, or R's arepresent in the molecule, the plurality of s's, L²'s, or R's may beidentical to or different from each other.
 2. A material for an organicelectroluminescent device according to claim 1, wherein in the generalformula (1), n represents 0 or
 1. 3. A material for an organicelectroluminescent device according to claim 1, wherein in the generalformula (1), the ring A represents a divalent carborane group C₂B₁₀H₁₀represented by the formula (1a).
 4. A material for an organicelectroluminescent device according to claim 2, wherein in the generalformula (1), the ring A represents a divalent carborane group C₂B₁₀H₁₀represented by the formula (1a).
 5. A material for an organicelectroluminescent device according to claim 1, wherein in the generalformula (1), L¹ and L² each independently represent a substituted orunsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, asubstituted or unsubstituted aromatic heterocyclic group having 3 to 17carbon atoms, or a linked aromatic group formed by linking 2 to 6aromatic rings selected from the aromatic hydrocarbon group and thearomatic heterocyclic group.
 6. A material for an organicelectroluminescent device according to claim 1, wherein in the generalformula (1), L¹ and L² each independently represent a substituted orunsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms,or a linked aromatic group formed by linking 2 to 6 aromatic ringsselected from the aromatic heterocyclic group.
 7. A material for anorganic electroluminescent device according to claim 1, wherein in thegeneral formula (1), n represents
 0. 8. An organic electroluminescentdevice having a structure in which an anode, an organic layer, and acathode are laminated on a substrate, wherein the organic layercomprises an organic layer containing the material for an organicelectroluminescent device of claim
 1. 9. An organic electroluminescentdevice according to claim 8, wherein the organic layer containing thematerial for an organic electroluminescent device comprises at least onelayer selected from the group consisting of a light-emitting layer, anelectron-transporting layer, and a hole-blocking layer.
 10. An organicelectroluminescent device according to claim 8, wherein the organiclayer containing the material for an organic electroluminescent deviceis a light-emitting layer containing a phosphorescent light-emittingdopant.
 11. An organic electroluminescent device according to claim 10,wherein an emission wavelength of the phosphorescent light-emittingdopant has an emission maximum wavelength at 550 nm or less.
 12. Anorganic electroluminescent device having a structure in which an anode,an organic layer, and a cathode are laminated on a substrate, whereinthe organic layer comprises an organic layer containing the material foran organic electroluminescent device of claim
 2. 13. An organicelectroluminescent device according to claim 12, wherein the organiclayer containing the material for an organic electroluminescent devicecomprises at least one layer selected from the group consisting of alight-emitting layer, an electron-transporting layer, and ahole-blocking layer.
 14. An organic electroluminescent device accordingto claim 12, wherein the organic layer containing the material for anorganic electroluminescent device is a light-emitting layer containing aphosphorescent light-emitting dopant.
 15. An organic electroluminescentdevice according to claim 12, wherein an emission wavelength of thephosphorescent light-emitting dopant has an emission maximum wavelengthat 550 nm or less.